Sunshades are generally known in the art for blocking or filtering light passing through an opening in a roof of a vehicle. The sunshade is generally disposed within a pair of guides and is movable between an open position where the opening is exposed and light is allowed to pass through, and a closed position in which the sunshade covers the opening for blocking or filtering the light coming through. Controlling frictional forces between the sunshade and the guides is needed to maintain consistent and smooth movement of the sunshade between the open and closed positions. In other words, when the frictional forces are inconsistent, an applied force required to move the sunshade between the open and closed positions is also inconsistent. It is desired that the applied force be relatively consistent for a user.
Various methods are taught by the prior art to control the frictional forces including the use of sliding shoes clipped along the edges of the sunshade. Other sunshades employ a curved panel portion to limit contact between the sunshade and the guides, see, e.g., U.S. Pat. No. 6,729,074. Relying on the curve or crown of the panel portion requires that the panel portion have sufficient strength and consistent physical properties that will maintain consistent frictional forces. In other words, variations in the curve or crown or in the physical properties of the sunshade could alter the frictional forces, and consequently, alter the applied force required to move the sunshade between the open and closed positions.
It is desirable for the sunshade to operate smoothly when moving between the open position and the closed position. It is also desirable to provide a process for making sunshades that allows quick and easy adjustment of the frictional force acting between the sunshade and the guides to maintain a consistent frictional force and required applied force during the manufacturing process. Several variables can contribute to varying the frictional force including the nature of the material (coefficient of friction), the weight, shape, and rigidity of the material, as well as many other factors.